1. Field of the Invention
The present invention relates t solid propellant disposal and recovery, and more particularly, to a method of recovering aluminum from waste composite aluminum-polymer mixtures.
2. Description of the Prior Art
A considerable amount of waste propellant is produced during the manufacture of solid propellant rocket motors. Such waste propellant is caused by a number of factors including, for example, the excess cast into the motor casing to compensate for shrinkage, from master-batches that do not meet specifications, and overage motors that are removed from service. Much of this waste propellant has been scrapped in the past and burned in open burning pits since the flammability and rubbery characteristics have been believed to prevent economical reclamation. The cost of burning waste propellant is considerable. In addition, open pit burning is hazardous and environmentally unacceptable.
Composite propellants normally consist of an oxidizer and aluminum powder cured in a polymeric binder system. There may also be various other ingredients for tailoring physical or ballistic properties. The oxidizer, generally ammonium perchlorate (AP), can be readily removed from the propellant leaving a residue consisting primarily of aluminum and polymer. Methods of removing, by shredding and leaching, ammonium perchlorate from composite propellants are disclosed in U.S. Pat. Nos. 3,451,789, issued to Meldon J. McIntosh on Jun. 24, 1969, 4,198,209, issued on Apr. 15, 1980 to Robert A. Frosch, Administrator of the National Aeronautics and Space Administration, with respect to an invention of Graham C. Shaw and Meldon J. McIntosh, and in the copending patent application Ser. No. 659,796, filed on Oct. 11, 1984 by Meldon J. McIntosh.
Studies have been made on the recovery by chemical solvent means of aluminum from propellants. The general approach has been to polymerize, or hydrolyze, the binder directly in the presence of the propellant ingredients. Catalysts or solvents have been used. These have enabled a partial breakdown of the binder system, but has allowed the recovery of only a small part of the aluminum present and that in an impure or contaminated state. In U.S. Pat. No. 4,229,182, issued on Oct. 21, 1980 to Robert A. Frosch, Administrator of the National Aeronautics and Space Administration with respect to an invention of Graham C. Shaw, there is disclosed a method of recovering aluminum powder from a solid propellant containing less than 15% oxidizer comprising dissolving the binder in an active transesterification solvent, filtering the solution, and then washing the recovered aluminum in a hydrocarbon solvent.
Due to the expense of the reaction techniques, the solvents required, and the necessary filtration and washing, the foregoing prior art methods for recovering aluminum from waste solid propellants have been ineffective, any recovery value of the aluminum being questionable when offset by the cost of recovery.
Thus, there is a need and a demand in the art for an improved method for recovering aluminum from aluminum-polymer mixtures. The present invention was devised to fill the technological gap that has existed for such a method.